There are various devices and techniques for reconstructing the anterior spinal column in the lumbar or thoracic spine. Specifically, a bone graft may be inserted between the vertebrae. The spine is then fused posteriorly with an implantable instrument of various designs.
However, the bone graft usually was obtained from the fibula or the iliac crest. Problems have arisen with donor site morbidity.
Also, various implantable devices for reconstruction of the spine comprise anterior plate and/or anterior rod systems.
Typically, one of two methods are used to reconstruct the anterior spine. Either an autologous bone graft or an allo graft is inserted into the defect, and a plate system is applied to the lateral side of the spine. Alternatively, a tubular xe2x80x9ccagexe2x80x9d may be inserted between vertebral bodies, and a plate may be applied, extending between intact vertebral bodies on either side of the defect. The cage may be filled with bone graft material such as bone fragments. The cage retains the material in place while the bone graft grows, fusing the two adjacent vertebral bodies.
By this invention, an integral, modular device is provided to replace a vertebral body that has been destroyed or must be removed because of fracture, tumor, infection or the like, while the device of this invention provides a site for an effective bone graft to fuse with intact, adjacent vertebral bodies, with both the device and the optional bone graft extending between the adjacent vertebral bodies and across the original space of the missing vertebral body. Also an improved technique of fastening the device in place is provided by this invention.
By this invention, an implantable, spinal, vertebral replacement device is provided. The device comprises a tubular cage for fitting into a space of a missing or damaged vertebral body. This tubular cage may be made of any implantable biomaterial such as stainless steel alloy, titanium, carbon fiber composite, bone, or the like, and can be used if desired to retain bone graft material in a desired position between intact vertebral bodies to form a fusion between the intact vertebral bodies across the site of the missing vertebral body. First and second transverse plates are respectively positioned at opposed ends of the tubular cage for supporting the respective ends of the tubular cage, and for pressing a plate face against an adjacent vertebral body in spinal column-supporting relation.
The transverse plates are each joined in transverse relation to typically a single vertebral attachment plate. This latter plate, in use, extends generally parallel to the spine, with the vertebral attachment plate defining screw holes for screw securance to at least one vertebral body adjacent to the space of the missing vertebral body.
Accordingly, by this invention both support and spacing of adjacent vertebral bodies is provided, along with retention and positioning of a tubular cage, which can retain bone graft material for the future growth of a strong bone graft after surgery.
In one embodiment, each transverse plate may be joined to a separate vertebral attachment plate, for attachment of the vertebral attachment plate to a separate, adjacent vertebral body positioned on an opposed side of the space left by the missing vertebral body. Cover plates may be carried on the vertebral attachment plate to cover the screw holes for screw securance to a vertebral body, and to also cover the screws occupying those holes. Thus, backing out of the screws in the holes after implantation of the device can be suppressed by the presence of such a cover plate.
As stated, the spinal replacement device of this invention may utilize a single vertebral attachment plate, to which both transverse plates are attached, with the vertebral attachment plate having screw holes for attachment to both of the adjacent, vertebral bodies.
As a further feature of this invention, the transverse plates may each have a peripheral, upstanding wall to surround and retain a respective supported end of the cage to prevent lateral cage movement. The peripheral, upstanding wall and cage are respectively dimensioned to preferably cause tight retention of the cage. The peripheral upstanding wall is preferably open at one end of the transverse plate, preferably the end facing the vertebral attachment plate, to receive the cage with lateral motion relative to the spinal column, this specific embodiment is particularly used with the system having the pair of vertebral attachment plates. Such a system can be used with cages of varying length, which slide into engagement with the peripheral, upstanding walls of the transverse plates.
Preferably, each transverse wall has a roughened face that faces the adjacent, intact vertebral body against which it presses in use. The roughened face may comprise a titanium mesh coating secured to the face of the plate that engages an end of the adjacent vertebral body, or it may be prepared by a variety of other, known techniques.
Also, each transverse plate preferably defines a central aperture, so that communication is available between the intact vertebral bodies and the bone graft material within the cage.
Some adjustability can be provided to the embodiment having a single vertebral attachment plate by providing the transverse plates with a hinged connection with the vertebral attachment plate, or even a frictional, spring-pinching connection between two flat surfaces of each transverse plate, respectively engaging opposed side surfaces of the vertebral attachment plate. Additionally, a bracket or strap may extend across an open end of the vertebral attachment plate with an aperture, for later application if desired after the cage has been positioned in the desired, surgical position, for better retention of each transverse plate with the vertebral attachment plate.
Preferably, the cage defines a slot at at least one end thereof, which slot is proportioned to receive a surgical distractor, for use during insertion of the cage into a position between the vertebral bodies.
Also, the cage may be elongated in one transverse dimension relative to its other transverse dimension, with the long dimension generally extending from side to side of the spine.
Accordingly, by the use of the above principles, a spinal replacement device is provided which can exhibit a unique combination of advantages, including a solid, firm retention of the entire system properly positioned in the spine, coupled with the facility to retain bone graft material in a position where growth can take place so that, after convalescence, the patient is less dependent upon the non-living implant, and more dependent on a more natural regrowth of bone in the spine.
As another aspect of the invention of this application, the spinal vertebral replacement device is advantageously secured to the intact vertebral bodies that are adjacent to the site of the missing vertebral body by means of screws that comprise an open, helical structure, generally in a manner similar to screws as disclosed by Kay U.S. Pat. No. 5,662,683 or European Patent Publication 0,374,088. These screws have some similarity to a simple corkscrew, being open at their center, rather than defining a metallic shaft in the manner of conventional screws. Several significant advantages are achieved when such a particular type of screw is used in combination with the spinal replacement device of this invention to secure the spinal replacement device to intact vertebrae. Among these advantages, as bone deflects, as can be expected in the spine of an active person, the open helix of such a screw better deflects with the bone, providing better load sharing over the length of the screw, to provide better screw fatigue life. As another advantage, an open helical screw does not require the previous removal of bone with a reaming drill, so that the screw does not displace a large plug of bone upon its insertion. Accordingly, much less bone is destroyed. Additionally, removal of the open, helical screw leaves only a narrow, elongated, helical path, whereas removal of an ordinary screw leaves a sizable hole in the bone, for significant weakening thereof.
Thus, since the open, helical screw destroys less bone upon insertion, a larger diameter, open helical screw can be used, when compared with a traditional bone screw. This larger diameter, open helical screw will have greater pull out strength, when compared with a corresponding, traditional bone screw positioned at the same site. It also may make possible in some circumstances the utilization of a single, open helical screw where otherwise two traditional bone screws would be necessary, with the result that substantially less bone is removed, and accordingly the vertebrae which receives the open, helical screw remains significantly stronger.
It may also be desired for a multiple shank open, helical screw to be used in accordance with this invention, where the screw comprises two or more independent, helical shanks which together define a central aperture, as disclosed, for example, in European Patent Publication 0,374,088.